if and when i start selective breeding i would look for a three things.
1. color. Color imo is a deciding factor for me. If i am looking to buy a snake i would want one with outstanding colors that last threw out the snakes life.

2. pattern. A snake with a unique pattern can be the deciding factor between one snake to another for me.

3. structure. Make sure the snake is structurly sound no deffects ect....
all of this was based on 2 cents